Short half-wave antenna with plural loading coils



y 5, 1966 R. o. BYKERK 3,259,901

SHORT HALF-WAVE ANTENNA WITH PLURAL LOADING GOILS Filed Jan. 2, 1962 1 v 2 Sheets-Sheet 1 INVENTOR.

RALPH 0- BYKERK ATTORNEY July 5, 1966 R. o. BYKERK 3,259,901

SHORT HALF-WAVE ANTENNA WITH PLURAL LOADING COILS Filed Jan. 2, 1962 2 Sheets-Sheet 2 m T c5 0 u. 3 u

g g, INVENTOR.

RALPH QBYKERK BY 244 ,33 w Rial/L64 ATTORNEY United States Patent.

Ohio

Filed Jan. 2, 1962, Ser. No. 163,532 3 Claims. (Cl. 343-749) This invention relates to antennas, more particularly to a short half-wave antenna.

Ideally, the length of a communication antenna should be exactly the length of a natural half-wave in the particular communication frequency being used. In the 27 mc. citizens band, for which the invention is preferably designed, the physical length of the natural half-wave is seventeen feet, four inches.

Where the antenna is to be used with mobile communication equipment, a seventeen foot, four inch radiating element is obviously undesirable and impractical. Moreover, section fifteen of the F.C.C. regulations requires that a mobile or base station communication antenna must not exceed sixty inches when used with unlicensed 100 milliwatt equipment.

In base station installations, which are permitted to use longer antennas, the available space often imposes limitations on the size antenna which can be used. For these reasons it is necessary to provide an antenna which in length is physically shortened, but electrically equivalent to the length of a natural half-wave.

Accordingly, it is an object of this invention to provide a new and improved physically shortened electrical halfwave antenna.

It is another object of this invention to provide a physically shortened half-wave antenna which is efficient and has a negligible decibel loss.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a partially exploded view of a completed antenna assembly employing the antenna of this invention and is exaggerated with respect to the vehicle upon which it is mounted;

FIGURE 2 is a schematic representation of the electrical configuration of the antenna of this invention;

FIGURE 3 is a foreshortened detail view of the antenna with parts broken away and removed; and

FIGURE 4 is a partial section with parts removed, taken at 44 of FIGURE 3.

Referring now to FIGURE 1, a complete antenna assembly is indicated generally by reference character 10. The antenna assembly includes an antenna structure 11, a supporting tube 12, and a mounting bracket assembly 13. For illustration purposes, the antenna assembly 10 has been exaggerated in size with respect to a supporting vessel or vehicle 46.

Referring again to FIGURE 1, the antenna 11 includes a whip radiating element 16 protruding from one end of a coil assembly 17. A connector 18 is provided at the other end of coil assembly 17. The connector 18 will be fastened to a coaxial cable for connection to mobile communication equipment carried on board the vehicle. A metallic ring 19 surrounds the coil assembly .at a point off center and near the connector end. A

plurality of radials 20 extend outwardly from the metallic ring 19 in the direction of the connector end of the coil assembly 17.

The electrical circuit configuration for the antenna 11 is shown in FIGURE 2. Electrically, the antenna 11 may be considered as an off-center fed single element antenna. Mutually coupled primary and secondary coils 29,

31 supply the antenna with radio frequency energy from a transmitter. The coils 29, 31 are positioned in the antenna element at a point off-center between its ends where the impedance of the antenna matches the output impedance of the transmission line.

.The energy supplied to the primary coil 29 induces a current in secondary coil 31. The current induced in secondary coil 31 travels in conductor 40 to an inductive loading coil 34. The inductive loading coil 34 performs the function of electrically lengthening the very short physical structure of the antenna. Current in the coil 34 travels to the whip 16 which is the radiating element. The mutually coupled coils 29, 31, the conductor 40, the coil 34 and the whip 16 are relatively dimensioned to be electrically equivalent to a natural quarterwave of the particular communication frequency in use.

Inasmuch as a counterpoise equivalent must be provided for the antenna to be independent of any associated area, a second loading coil 35 and the capactive inductive radials 20 are provided as a very short, tuned counterpoise electrically equivalent to a quarter-wave length of the frequency in use.

The physical structure of the coil assembly 17 is shown in FIGS. 3 and 4. FIG. 4 shows the coil form portion of a partially completed coil assembly. The coil form 21 is a solid rod and made preferably of a synthetic plastic material. A brass end cap 22 is mechanically secured to one end of coil form 21. A connector assembly mechanically secured at the other end of the coil form 21 is indicated by the general reference number 23.

The connector assembly 23 includes a center pin connector 24 and an outer shield 25. The pin connector 24 is electrically insulated from the shield 25 by the insulation material 26. When the connector assembly 23 is secured to the end of the coil form 21, the pin connector 24 extends into the center of the coil form 21 so as to be axially coextensive therewith.

A sleeve member 28 is mechanically secured around the coil form 21 at a point off-center and near the connector end. A connector screw 27 is provided and is mounted in theouter surface of the coil form so as to contact the inserted end of the pin connector 24.

FIGURE 3 shows a completed coil assembly. The primary coil 29 is wound on the coil form 21 near the connector end. One end of the primary coil 29 is soldered on the shield portion 25 of the connector assembly at 30. The other end of the primary coil 29 is electrically connected to the pin connector 24 by means of the connector screw 27. The secondary coil 31 is coupled therewith. One end of the secondary coil 31 is also soldered to the shield 25. The other end of the secondary coil 31 is bent around eyelet 32 and extends along the length of the coil form 21 to eyelet 33 near the end cap 22. The inductive loading coil 34 provided to electrically lengthen the antenna is wound on the coil form 21 adjacent the eyelet 33. The free end of the coil 34 is soldered to the end cap 22 at 43.

A socket is provided in the top of the end cap to receive the whip element 16. The whip element 16 is inserted into the socket and secured to the end cap 22 by set screw 41. Thus the end cap 22 serves to electrically connect the whip element 16 to the loading coil 34.

As suggested above, in order to properly tune the antenna the second inductive loading coil 35 is wound around the coil form 21 in a lumped position in that it is located between the primary coil 29 and the sleeve 28. This lumped arrangement of the coil 35 with the mutually coupled coils 29, 31 greatly shortens the antenna structure. The lumped arrangement also assures that the quality factor of loading coil 35 will not be destroyed.

One end 44 of the second loading coil 35 is soldered to the shield 25 to form a common base for the antenna with the similarly soldered ends of the mutually coupled coils 29, 31. The other end 45 of the second loading coil 35 is soldered to the sleeve 28.

A metallic ring 19, is removably secured around the sleeve 28 by a set screw 26. A plurality of radials 20 (FIGS. 1 and 3) extend outwardly from the metallic ring 19. The length and number of radials will depend upon the capacitance and the inductance needed to tune the couunterpoise formed by the radials 20 and the loading coil 35.

A supporting sleeve 37 is provided to rigidly secure the antenna to the supporting tube 12 (FIG. 1). The supporting sleeve 37 is removably secured to the connector end of the coil form by means of set screws 46.

Plastic jackets 38 and 42 are provided to weatherseal the completed unit. The jacket 38 surrounds the coil assembly between the end cap 22 and the metallic ring 19. The jacket 42 surrounds the coil assembly between the metallic ring 19 and the supporting sleeve 37.

The distribution of current and voltage along the antenna is also shown in FIGURE 2. It is to be noted that the current i is at a maximum in the working area of the coils 29, 31 and drops ofi sharply towards the end of coil 34. The distribution of voltage v is just opposite to that of the current. The voltage is low along the working area of the antenna and rises sharply at the end of the coil 34 to a maximum at the end of the whip radiating element.

The current and voltage curves of FIG. 2 appear to be non-sinusoidal. This factor is brought about by the mechanical arrangement of the inductors 34, 35 which are primarily the current areas of the antenna. In actual electrical configuration, however, a sinusoidal wave does stand on the antenna as an electrical half-wave as normally expected in a tuned circuit representing a half-wave antenna.

Although the specification describes the invention in detail it is believed to comprise essentially a physically shortened, half-wave antenna having means to feed radio frequency energy to the antenna at a point off-center between the antenna ends. The antenna includes a first impedance means to electrically lengthen the top half of the antenna including the oft-center feeder point to a quarter-wave length of the frequency F and a second impedance means to electrically lengthen the counterpoise to be equivalent to a quarter-wave length of the frequency F Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.

What is claimed is:

1. An antenna comprising, a top half portion including a radiating element, first impedance means connected to said top half portion to electrically lengthen it to a quarter-wave length of the frequency in use, a counterpoise portion, feeder means, electrically connected off center between said top half portion, and said counterpoise portion to transmit radio frequency energy to and from the antenna, said counterpoise portion including a second impedance means mechanically disposed between said first impedance means and said off-center feeder means to electrically lengthen the counterpoise portion to be equivalent to a quarter-wave length of the frequency in use.

2. A physically shortened half-wave antenna element for the frequency F comprising a connector having a shield portion and a central pin connector portion, a primary coil, a secondary coil inductively coupled with said primary coil, one end of each of said primary and said secondary coils being connected to the shield portion of said connector, the other end of the primary coil being nected to the second end of the conductor and the other end connected to the antenna whip, a second loading coil, said second loading coil being disposed between said secondary coil and said first loading coil but substantially closer to said secondary coil and having one end connected to the shield portion of said connector to form a common antenna base with the similarly connected ends of the primary and secondary coils, at least one radial extending in a direction opposite to that of the antenna whip and connected to the other end of said second loading coil, said primary and secondary inductively coupled coils, said conductor means, said first loading coil and the antenna whip all being relatively dimensioned so as to be electrically equivalent to the natural quarter-wave length of the frequency F said second loading coil and said at least one radial being relatively dimensioned to provide a very short tuned counterpoise electrically equivalent to the quarter-wave length of the frequency F 3. A physically shortened electrical half-wave antenna for a communication frequency F comprising, a coil form, said coil form comprising a solid nylon cylinder member having a first and second end, an end cap, said end cap being mounted on the first end of said coil form connector having an outside shield portion and an elon-i gated pin connector center portion insulated from the outside shield portion, said connector being mounted on said second end of said coil form so that the pin connector portion extends into a center bore in said coil form, a Sleeve member being circumferentially mounted on said coil form between said end vcap and said connector but 1 substantially closer to the connector, a connector screw,

said connector screw being removably mounted intermediate the connector and the sleeve member in the outside surface of said coil form andengaging the end of the elongated pin connector, a primary coil being wound around the coil form near the connector and having a first and second end, said first coil end being soldered to the shield portion of said connector and said second coil end being removably secured to said elongated pin connector by means of said connector screw, a secondary coil being wound around said coil form near the connector so as to be interwound between the turns of said primary coil to provide a mutual coupling therewith, said secondary coil having one end soldered to the shield portion of said connector, a conductor being connected to the other end of said secondary coil and extending, substantially, along the entire length of said coil form to a point near said end cap, a first loading coil, said first loading coil being wound around said coil form near the first end thereof and having one end connected to said conductor means and the other end soldered to said end cap, a second loading coil, said second loading coil being wound around said coil form between said primary coil and said sleeve member, one end of said second loading coil being soldered to said shield portion of the connector to form .with the similarly soldered ends of said primary and said secondary coils a common base for the radiating element, the other end of said second loading coil being soldered to said sleeve member, a metallic ring member,

said metallic ring member being removably mounted cir-L to be electrically equivalent to the natural quarter-wave length of the frequency F the second loading coil and the radials being relatively dimensioned to provide a very short tuned counterpoise electrically equivalent to the quarter-wave length for the frequency F a second and supporting sleeve member, said supporting sleeve member surrounding said connector and being removably secured to the shield portion thereof, said supporting sleeve memher being adapted to be mounted on a supporting tube which carries the antenna in its preferably vertical operating position, a first and second plastic jacket surrounding said coil form and the coils wound thereon, and weathersealing the entire coil assembly, said first plastic jacket extending between said end cap and said metallic ring member, said second plastic jacket extending between said metallic ring member and said supporting sleeve member.

References Cited by the Examiner UNITED STATES PATENTS 1,314,095 8/ 1919 Reuthe 343750 1,697,948 1/ 1929 Chireix 343--847 2,881,428 4/ 1959 Batchelor 343750 X FOREIGN PATENTS 842,533 7/1960 Great Britain.

OTHER REFERENCES End Loaded Elements Construction by Hatfield, QST, April 1958, pages 28, 29, 150.

15 ELI LIEBERMAN, Acting Primary Examiner.

HERMAN KARL SAALBACH, Examiner. 

2. A PHYSICALLY SHORTENED HALF-WAVE ANTENNA ELEMENT FOR THE FREQUENCY F1 COMPRISING A CONNECTOR HAVING A SHIELD PORTION AND A CENTRAL PIN CONNECTOR PORTION, A PRIMARY COIL, A SECONDARY COIL INDUCTIVELY COUPLED WITH SAID PRIMARY COIL, ONE END OF EACH OF SAID PRIMARY AND SAID SECONDARY COILS BEING CONNECTED TO THE SHIELD PORTION OF SAID CONNECTOR, THE OTHER END OF THE PRIMARY COIL BEING REMOVABLY SECURED TO THE CENTRAL PIN CONNECTOR PORTION OF SAID CONNECTOR, A CONDUCTOR HAVING A FIRST AND SECOND END, THE OTHER END OF THE SAID SECONDARY COIL BEING CONNECTED TO SAID FIRST END OF THE CONDUCTOR, AN ANTENNA WHIP, A FIRST LOADING COIL, SAID FIRST LOADING COIL HAVING ONE END CONNECTED TO THE SECOND END OF THE CONDUCTOR AND THE OTHER END CONNECTED TO THE ANTENNA WHIP, A SECOND LOADING COIL, SAID SECONDARY LOADING COIL BEING DISPOSED BETWEEN SAID SECONDARY COIL AND SAID FIRST LOADING COIL BUT SUBSTANTIALLY CLOSER TO SAID SECONDARY COIL AND HAVING ONE END CONNECTED TO THE SHIELD PORTION OF SAID CONTAINER TO FORM A COMMON ANTENNA BASE WITH A SIMILARLY CONNECTED ENDS OF THE PRIMARY AND SECONDARY COILS, AT LEAST ONE RADIAL EXTENDING IN A DIRECTION OPPOSITE TO THAT OF THE ANTENNA WHIP AND CONNECTED TO THE OTHER END OF SAID SECOND LOADING COIL, SAID PRIMARY AND SECONDARY INDUCTIVELY COUPLED COILS, SAID CONDUCTOR MEANS, SAID FIRST LOADING COIL AND THE ANTENNA WHIP ALL BEING RELATIVELY DIMENSIONED SO AS TO BE ELECTRICALLY EQUIVALENT TO THE NATURAL QUARTER-WAVE LENGTH OF THE FREQUENCY F1, SAID SECOND LOADING COIL AND SAID AT LEAT ONE RADIAL BEING RELATIVELY DIMENSIONED TO PROVIDE A VERY SHORT TUNED COUNTERPOISE ELECTRICALLY EQUIVALENT TO THE QUARTER-WAVE LENGTH OF THE FREQUENCY F1. 